[howd]

Hey guys: I have 1998 Okuma-Howa HL-20 with 18T Fanuc controls. I had been having problems with alarm 751 (AL-27). As best I can tell, that's serial spindle encoder disconnect. I was loosing the 1 signal, cause it would rapid to position, then just sit there. So I bit the BIG bullet, and installed a new encoder on the spindle. Now I 'think' it may have doing this before encoder install, but I know it's doing it now. The spindle speed on the CRT is going nuts. Before the spindle is even turning. Even in E stop (nothing happenin but the fans turning), the speed goes nuts. Went into the Diagnostics, and found at 417, the spindle one position coder is way more whacked out than even the CRT numbers. So I removed the fan from the spindle motor, and that coder is in pristine order. Been moving wiring around and looking things over, still no clues. Had an electronic guru over, and we had a lab scope hooked to the box that the encoders feed to (both boxes), and no sign of weird signals down there. Having wondered if this was just some weird signal to the CRT, I did do some turning with it. G96 CSS caused the 751 (AL-27) alarm to come back. The 1 for the threading signal was definitely working, but threading feed rate was off the chart and varied (like the feed was trying to keep up with a wild spindle speed!). Spindle motor encoder? Spindle amp?

[Rocksalt]

I may be mistaken, but I think the encoder you are looking for is attached to the headstock and a small belt drives the encoder. If the numbers are moving all around it could mean the wire(s) are broken and floating. Ring out the cable from the encoder to the connection point.

[howd]

Hi Rocksalt: The spindle encoder for the spindle is a seven inch bracket that encircles the spindle drive. The encoder pickup heads (there are 2), are mounted to that. they are positioned 180 degrees apart. the little computer looking box, the pickup heads, bracket, encoder ring, and wiring, are all brand new. You get it all, when you order the encoder. My reasonable assumption is: the encoder(s) on the spindle itself are for position and the reference pulse for threading. And that the encoder on the spindle motor is for rpm. But that's all assumption, as the books don't confirm that. I can't see why they would have a position encoder on the motor, as belt slippage to the spindle would render that information useless; but that's what it looks like Fanuc is calling it. And IF it's just an RPM pickup, why on earth would it be such a complicated affair? Looks just like the spindle encoder, but just one pickup head. Just praying it isn't another $5,000!!!

[Rocksalt]

If its an AC spindle motor the resolver on the motor is for commutation. The external encoder is for threading and RPM. Did you ring out the wires from the encoder to the destination?

[underthetire]

So you have a built in type encoder (tooth or magnetic). Fanuc has a breakout board that allows you to put a scope on it. Some of the amplifiers (black box) also have test point in them. I would first suspect the gap is set wrong between the sensor and ring. I also have seen random readings when the rear spindle support bearing starts to fail.

[howd]

Hey Rocksalt: It is an AC spindle motor, at least there's 3 leads carrying AC current to the motor. I was in the process of checking the wiring from the spindle encoder black box to the spindle amplifier this morning. Had the spindle turning at 100rpm in MDI. Unplugged the encoder lead (JY5) from the board, and nothing changed, as far as the CRT speed display. Still bouncing rapidly all over the place. Course, it was doing that with the spindle sitting still. Plugged JY5 back in, and took JY2 (lead from spindle motor) off, and that set an immediate alarm. AL-01, which is spindle motor overheat. And Underthetire, I believe that the black box is a signal modifier to the spindle amp. Inside the box are some tabs that look like the perfect place to pull scope readings from. Marked B3, A3, B1, A1, Z, VRM, OV, 5V. It looks as though the spindle motor encoder and the spindle encoder use the same signal modifier box(s). On the printed circuit board are what look like adjustable dashpots, that are adjusted with a Phillips screw driver. If I only knew which one ta crank on.....